The synthesis and characterization of heterobimetallic (?5-indenyl)[1-Me2Si(tBuN)TiCl2]{3-[N,N-bis(2-(ethylthio)ethyl)amine]CrCl3} ({Ti-C0-Cr} ) and (?5-indenyl)[1-Me2Si(tBuN)TiCl2]{3-C6H12-[N,N-bis(2-(ethylthio)ethyl)amine]CrCl3} ({Ti-C6-Cr} ) are presented. In ethylene homopolymerization, both of {Ti-C0-Cr}  and {Ti-C6-Cr}  afford linear low-density polyethylene (LLDPE) using ethylene as the only feed, similar as the analogue (?5-indenyl)[1-Me2Si(tBuN)TiCl2]{3-C2H4-[N,N-bis(2-(ethylthio)ethyl)amine]CrCl3} ({Ti-C2-Cr} ). {Ti-C0-Cr}  produces higher molecular weights and branching density polyethylene vs {Ti-C2-Cr}  under identical conditions, while {Ti-C6-Cr}  acts in a reverse manner. In the ethylene + 1-pentene competition experiments, {Ti-C0-Cr}  incorporates n-propyl branches as low as 5.5% in total branches, while the numbers for {Ti-C2-Cr}  and {Ti- C6-Cr}  are 34.8% and 55.1%, respectively. With iBu3Al/Ph3CB(C6F5)4 as the activator/cocatalyst, linear polyethylene without branches detectable was yielded for all three catalysts. When polar solvent C6H5Cl is used as the polymerization medium, higher activity and lower product branching densities are observed. Both homopolymerization and copolymerization results argue that achievable Ti���Cr spatial proximity significantly influences chain transfer rates and selectivity for comonomer enchainment and that such proximity effects are highly cocatalyst and solvent sensitive.

Heterobimetallic effects for enhanced a-olefin incorporation in ethylene polymerization catalysis

247th National Meeting (2014)

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